Delta-sigma modulators are electronic circuits for performing analog-to-digital conversion, digital-to-analog conversion, or digital-to-digital conversion. A basic delta-sigma modulator for analog-to-digital conversion includes an integrator for integrating a difference between an input signal and a feedback signal. The output of the integrator is supplied to a threshold amplifier. The output of the threshold amplifier is input to an impulse circuit, which provides the feedback signal for integration. The output of the threshold amplifier is also supplied to a counter, which completes the digital conversion process.
Higher-order delta-sigma modulators for analog-to-digital conversion may include additional integrators with additional feedback loops. Higher-order delta-sigma modulators allow additional zeroes to be obtained in a noise transfer function. Single-order delta-sigma modulators are generally stable, and second-order modulators can also be designed as generally stable. However, higher-order delta-sigma modulators are generally unstable. Conventionally, stability analysis is performed on higher order delta-sigma modulators to determine what conditions cause the higher-order delta-sigma modulator to become unstable. Instability problems increase as the order of the delta-sigma modulator increases beyond the second order, such as with a third-order or higher delta-sigma modulator.
One conventional solution to the instability problem is feedback steering. In the side-car approach, an alternate lower-order delta-sigma modulator is constructed along-side a higher-order delta-sigma modulator. For example, a second-order delta-sigma modulator may be constructed alongside a fourth-order delta-sigma modulator. When the higher-order feedback loop becomes unstable, an output of the side-car stage of the delta-sigma modulator was substituted for the higher-order feedback loop. The side-car approach provides an alternative operation for the delta-sigma modulator, but does not reduce the instability of the delta-sigma modulator.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electronic devices, particularly in consumer-level devices. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.